In a number of different ways it is possible to accomplish a reciprocating movement or force, which it may be desirable to transform into a unidirectional movement or force. A relatively recently developed technique is to utilize materials having magnetostrictive properties. Magnetostriction means that a material changes its dimensions when exposed to a magnetic field.
Materials with such properties are typically alloys with rare earth metals, an alloy with terbium and iron being available under the name Terfenol. This material Terfenol has a very high magnetostriction, namely up to 0.2% at a magnetic field with a field strength of appr. 3000 oersted, and a very fast response.
Due to the magnetostriction a Terfenol rod exposed to a pulsating magnetic field and prestressed for accomplishing a return to original shape will have reciprocating length and accordingly exert an reciprocating force.
In order to utilize this reciprocating movement or force in a practical force actuator this movement has to be transformed--by a movement transforming device into a unidirectional movement of a push rod or the like in the actuator.